Electrophotographic photoreceptor and electrophoto-graphic apparatus equipped with the same

ABSTRACT

A top surface layer of an electrophotographic photosensitive element (e.g., a charge-transporting layer) is rendered to contain a cyclic polysilane represented by the following formula (1). 
     
       
         
         
             
             
         
       
     
     In the formula, R 1  and R 2  are the same or different from each other and each represents a group such as an alkyl group, an aryl group, and “m” denotes an integer of not less than 4. 
     The cyclic polysilane may be a copolysilane. The content of the cyclic polysilane may be about 0.01 to 10% by weight relative to the whole components of the top surface layer.

CROSS REFERENCE TO RELATED APPLICATION

This is the U.S. National Stage of PCT/JP03/09163, filed Jul. 18, 2003,which in turn claims priority to Japanese Patent Application No.2002-214336, filed on Jul. 23, 2002, both of which are incorporatedherein in their entirety by reference.

TECHNICAL FIELD

The present invention relates to an electrophotographic photosensitiveelement excellent in durability and capable of providing a highdefinition image over a long period, and an electrophotographicapparatus provided with the electrophotographic photosensitive element.

BACKGROUND ART

Since a surface of an electrophotographic photosensitive element (asurface of a photosensitive layer) undergoes various electrical,chemical or mechanical stresses due to processes such aselectrification, exposure, development, transference, and cleaning [forexample, wear (or abrasion) and scarring of the surface layer due torepetitive use, and oxidization and degradation of the surface due toozone generated by corona discharge], durability is required for thesurface to these stresses. In particular, along with recentpopularization of a roller electrification system, it has become aproblem that the surface is worn down accompanied with cutting ofbonding of molecules on the photosensitive layer surface caused by arcdischarge. Further, demands for full-coloration or speedup of a printerand miniaturization of a photosensitive drum bring about overlap ofconditions facilitating stresses in the photosensitive element surfaceas described above. Therefore, improved durability of theelectrophotographic photosensitive element has been further required.

In order to solve such problems concerning the photosensitive elementsurface, improvement in properties such as surface abrasion, a releaseproperty of toner, and a cleaning property is attempted by adding asilicone-series compound or fluorine-containing compound which has asmall surface free energy and is excellent in water repellency orlubricity [for example, Japanese Patent Application Laid-Open No.132954/1986 (JP-61-132954A), Japanese Patent Publication No. 113779/1995(JP-7-113779B)].

However, since these compounds are low in compatibility ordispersibility to a resin constituting a photosensitive layer of thephotosensitive element and inferior in transparency of a top surfacelayer thereof, it is difficult to obtain a high definition image.Moreover, these compounds incline to be maldistribute in the vicinity ofthe top of the surface layer. Thereby, even if only the top surfacelayer is slightly worn by friction or sliding in the surface, a propertysuch as lubricity is drastically reduced or a cleaning property is fastdeteriorated by bleeding out of these compounds with passage of time.Further, it is difficult to obtain a sharp image over a long period bysuch deterioration in the lubricating or cleaning property.

Meanwhile, Japanese Patent Application Laid-Open No. 178652/1992(JP-4-178652A) discloses a method for improving a durability or arepeating property of a photosensitive element, which comprises adding apolysilane or a copolysilane to a photosensitive layer. This documentdescribes that (i) as the polysilane, there may be used a polysilane orcopolysilane whose end is blocked with an alkyl group or the like andwhich has a relatively high molecular weight (in Examples, anumber-average molecular weight of 18000, or 23000); (ii) the mixingratio of the polysilane is preferably about 20% to 80% relative to abinder resin constituting the photosensitive layer [e.g., a poly(methylmethacrylate)]; and (iii) in a single-layered photosensitive elementhaving a combination of a charge transport function and a chargegeneration function, it is preferred to add 3 to 7 parts by weight ofthe polysilane and 3 to 7 parts by weight of the binder resin to 1 to 10parts by weight of a charge-generating substance.

According to the method of this document, however, since the polysilaneinferior to the binder resin in mechanical strength is used in greatquantities, this method not only is disadvantageous in cost but alsoaccelerates wear (abrasion) of the photosensitive layer. Moreover, theuse of the polysilane having a high-molecular weight gives inadequatecompatibility or dispersibility to the resin, deteriorates transparencyof the photosensitive layer, and has the potential of impairingsharpness (or clearness) in an image.

It is therefore an object of the present invention to provide anelectrophotographic photosensitive element improving water repellencyand lubricity (lubricating property) thereof and forming a high qualityimage (or picture image) over a long period, as well as a method forproducing the same.

It is another object of the present invention to provide anelectrophotographic photosensitive element which has excellentdurability without deterioration in a property such as lubricity or acleaning property even in the case of wearing a surface layer thereof,and a method for producing the same.

It is still another object of the present invention to provide anelectrophotographic photosensitive element which can realize a highdefinition image without deterioration in mechanical strength ortransparency and can ensure conservation of a high-quality imageproperty even with prolonged application, a method for producing thesame, and an electrophotographic apparatus provided with theelectrophotographic photosensitive element.

DISCLOSURE OF INVENTION

The inventors of the present invention made intensive studies to achievethe above objects and finally found that a small amount of a specificpolysilane added to a top surface layer of an electrophotographicphotosensitive element ensures conservation of lubricity or a cleaningproperty over a long period, and realizes a high definition image. Thepresent invention was accomplished based on the above findings.

That is, the electrophotographic photosensitive element of the presentinvention comprises at least a top surface layer containing apolysilane, wherein the polysilane comprises a cyclic polysilanerepresented by the following formula (1):

wherein R¹ and R² are the same or different from each other and eachrepresents a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxygroup, an alkenyl group, a cycloalkyl group, a cycloalkyloxy group, acycloalkenyl group, an aryl group, an aryloxy group, an aralkyl group,an aralkyloxy group, or a silyl group; the alkyl group, the alkoxygroup, the alkenyl group, the cycloalkyl group, the cycloalkyloxy group,the cycloalkenyl group, the aryl group, the aryloxy group, the aralkylgroup, the aralkyloxy group, or the silyl group may have a substituent;“m” denotes an integer of not less than 4; and R¹ and R² may varydepending on the coefficient “m”, respectively.

In the formula (1), at least one of R¹ and R² may be an aryl group (suchas a phenyl group), and “m” may be an integer of about 4 to 10 (e.g.,about 4 to 8, particularly 5).

The cyclic polysilane may be a copolysilane. Such a cyclic polysilanemay be, for example, represented by the following formula (1a):

wherein R^(1a) and R^(2a) each represents an aryl group which may have asubstituent; R^(1b) and R^(2b) are the same or different from each otherand each represents an alkyl group which may have a substituent, acycloalkyl group which may have a substituent, or an aryl group whichmay have a substituent; provided that both R^(1b) and R^(2b) are notcoincidentally an aryl group which may have a substituent; m1 denotes aninteger of not less than 1; m2 denotes 0 or an integer of not less than1; and m1+m2 denotes an integer of not less than 4.

In the formula, R^(1a) and R^(2a) each may be a C₆₋₁₀aryl group.Moreover, a combination of R^(1b) and R^(2b) may be, for example, (1) acombination of a C₁₋₄alkyl group and a C₁₋₄alkyl group, (2) acombination of a C₁₋₄alkyl group and a C₆₋₁₀ aryl group, (3) acombination of a C₁₋₄alkyl group and a C₅₋₈cycloalkyl group, or (4) acombination of a C₆₋₁₀ aryl group and a C₅₋₈cycloalkyl group.Incidentally, m1 may be an integer of about 1 to 10 (e.g., about 1 to8), m2 may be an integer of about 0 to 10 (e.g., about 0 to 8), andm1+m2 may be about 4 to 12 (e.g., about 4 to 10).

Further, the polysilane may be a polysilane mixture containing a cyclicpolysilane.

The electrophotographic photosensitive element of the present inventioncomprises at least both of an electroconductive support and aphotosensitive layer, wherein the photosensitive layer usually comprisesat least the following components: a charge-generating agent, acharge-transporting agent, and a binder resin. The photosensitive layermay comprise a charge-generating layer, and a charge-transporting layerformed on the charge-generating layer. A surface protection layercontaining the cyclic polysilane may be formed on the photosensitivelayer. Moreover, the content of the cyclic polysilane may be about 0.01to 10% by weight (e.g., about 0.01 to 5% by weight) relative to thewhole components of the top surface layer. For example, the top surfacelayer comprises an outer surface layer of the photosensitive layer or asurface protection layer of the photosensitive layer, and the proportionof a cyclic homo- or copolysilane having at least a diarylsilane unitmay be about 0.01 to 3% by weight relative to whole components of thetop surface layer.

The electrophotographic photosensitive element of the present inventionmay be produced by forming at least a photosensitive layer on anelectroconductive support to obtain the electrophotographicphotosensitive element, wherein the cyclic polysilane may beincorporated into at least a top surface of the electrophotographicphotosensitive element.

The present invention also includes an electrophotographicphotosensitive element composition, which comprises a component for anouter surface layer of a photosensitive layer or a component for asurface protection layer of a photosensitive layer, and a cyclicpolysilane. The composition may comprise, for example, depending on astructure of the photosensitive layer, a binder (e.g., apolycarbonate-series resin), a cyclic polysilane, and at least onemember selected from the group consisting of a charge-generating agentand a charge-transporting agent.

The present invention further includes an electrophotographic cartridgeand an electrophotographic apparatus, which are provided with theelectrophotographic photosensitive element.

Throughout this specification, the generic name for a polysilane and anoligosilane is a “polysilane”. The cyclic polysilane is sometimesgenerically called a “polysilane”, simply.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing an embodiment of a form ofa polysilane contained in a top surface layer.

FIG. 2 is a schematic sectional view showing another embodiment of aform of a polysilane contained in a top surface layer.

FIG. 3 is a schematic sectional view showing still another embodiment ofa form of a polysilane contained in a top surface layer.

FIG. 4 is a schematic sectional view showing an embodiment of anelectrophotographic apparatus provided with the electrophotographicphotosensitive element of the present invention.

FIG. 5 is a figure showing a result of analysis of a compositiondistribution of a thin coat obtained in Example 1.

DETAILED DESCRIPTION OF THE INVENTION

[Electrophotographic Photosensitive Element]

The electrophotographic photosensitive element of the present inventioncomprises at least both of an electroconductive support and aphotosensitive layer. At least the top surface layer of theelectrophotographic photosensitive element comprises a cyclicpolysilane.

Incidentally, the cyclic polysilane may be included in at least the topsurface layer. For example, the polysilane may be included only in thetop surface layer of the photosensitive layer, or may be includedthroughout the photosensitive layer in accordance with the layerstructure of the photosensitive layer or others.

(Electroconductive Support)

As the electroconductive support, there may be used a conventionalelectroconductive support in a field of an electrophotographicphotosensitive element. For example, such a support may include asupport comprising a substrate (e.g., a plastic, and a paper) and anelectroconductive coat formed thereon with a means such as deposition orsputtering; a support comprising a substrate (e.g., a plastic, and apaper) and an electroconductive fine particle coated on the substratethrough a binder (e.g., a plastic, and a paper); and a metal support(e.g., an aluminum plate).

As a material for the electroconductive coat or electroconductive fineparticle, for example, there may be mentioned a metal (such as aluminum,nickel, chromium, nichrome, copper, silver, gold, platinum, or an alloyof such a metal), a metal oxide (such as tin oxide or indium oxide), andgraphite.

The form (or shape) of the electroconductive support (or the substrate)may be a film (or sheet), a tube, or a (circular) cylinder. The tubularelectroconductive support may include a metal tube obtained by molding aplate or matte of a metal (e.g., the above-exemplified metal, an alloysuch as an aluminum base alloy or a stainless steel) into a cylindricalform by an extrusion process, a drawing process, or other process, andsubjecting the molded product to a surface finishing (e.g., cutting,superfinishing, and grinding).

The thickness of the electroconductive support is not particularlylimited to a specific one, and for example, may be about 0.05 to 10 mm,preferably about 0.05 to 8 mm, and preferably about 0.1 to 5 mm.Moreover, in the case where the electroconductive support is in the formof a tube or cylinder, the diameter of the tube or cylinder may forexample be about 5 to 300 mm, preferably about 10 to 200 mm, and morepreferably about 20 to 150 mm.

(Undercoat Layer or Charge Injection-blocking Layer)

In the electrophotographic photosensitive element of the presentinvention, if necessary, an undercoat layer (charge injection-blockinglayer) may be formed between the electroconductive support and thephotosensitive layer (or on the electroconductive support). Theformation of the undercoat layer ensures to block charge injection fromthe photosensitive layer, and to improve adhesiveness of thephotosensitive layer to the electroconductive support. The undercoatlayer may comprise a binder having high adhesiveness to theelectroconductive support, for example, a binder such as a polyvinylalcohol, a polyvinyl acetal such as a polyvinyl butyral, aheterocycle-containing resin (e.g., a polyvinyl pyridine, a polyvinylpyrrolidone, and a poly-N-vinylimidazole), a polyethylene oxide, acellulose ether, or a cellulose ester (e.g., a methyl cellulose, anethyl cellulose, and a cellulose acetate), an ethylene-acrylic acidcopolymer, an ionomer resin, an acrylic resin, a polyamide-series resin(e.g., a linear polyamide-series resin, and a copolyamide), a naturalpolymer or a derivative thereof (e.g., a glue, a gelatin, and a casein),a phenol resin, an epoxy resin, or a silane coupling agent.

The undercoat layer may be usually formed by dissolving the binder in asolvent (e.g., an alcohol such as methanol), and coating the resultantsolution on the electroconductive support. The thickness of theundercoat layer may be about 0.1 to 5 μm, and preferably about 0.2 to 3μm.

(Photosensitive Layer)

The photosensitive layer may usually comprise a charge-generating agentand a charge-transporting agent. The form of the photosensitive layerformed or laminated on the electroconductive support (or undercoatlayer) may be classified broadly into two categories: one is so-calledlaminated photosensitive layer comprising a layer having a chargegeneration function (a charge-generating layer) and a layer having acharge transport function (a charge-transporting layer); and the otheris so-called single-layered photosensitive layer having a combination ofa charge generation function and a charge transport function. Each ofthese functional layers (the single-layered photosensitive layer, thecharge-transporting layer, and the charge-generating layer) may be asingle layer, or may comprise a plurality of layers (e.g., two to fivelayers).

Incidentally, in the laminated photosensitive layer, a layer located onthe front face side (e.g., a charge-transporting layer or acharge-generating layer) may constitute a top surface layer. In thesingle-layered photosensitive layer, the whole photosensitive layer mayconstitute a top surface layer. Moreover, when the functional layer (thefunctional layer in the surface side) comprises a plurality of layers, alayer located on the top surface side in the functional layer mayconstitute a top surface layer.

(Laminated Photosensitive Layer)

In the laminated photosensitive layer, the order (or sequence) to belaminated of the charge-generating layer and the charge-transportinglayer on the support is not particularly limited to a specific one. Thecharge-generating layer may be laminated on the charge-transportinglayer, or the charge-transporting layer may be laminated on thecharge-generating layer. The charge-transporting layer may be usuallyformed or laminated on the charge-generating layer. In such an order oflamination, the thickness of the charge-transporting layer is usuallylarger than that of the charge-generating layer so that a top surfacelayer containing a polysilane can be formed with the charge-transportinglayer. Thereby, the laminated photosensitive layer having such an orderhas a high durability for a long period even when the layer is worn, andis suitable for use.

In the laminated photosensitive layer, the charge-generating layer maycomprise a charge-generating agent alone, or a charge-generating agentand a binder resin.

The charge-generating agent may include, for example, an inorganiccharge-generating agent such as selenium or an alloy thereof, or cadmiumsulfide; and an organic charge-generating agent such as a phthalocyaninepigment, an azo pigment, a bisazo pigment, a trisazo pigment, a pyryliumdye, a thiopyrylium dye, a quinacridone pigment, an indigo pigment, apolycyclic quinone pigment, an anthanthrone pigment, a pyranthronepigment, a cyanine pigment, or a benzimidazole pigment. Thesecharge-generating agents may be used singly or in combination.

Among these charge-generating agents, the preferred compound may includea phthalocyanine-series pigment (a metal-free phthalocyanine pigment anda metal phthalocyanine pigment). The metal-free phthalocyanine mayinclude, for example, an α-type metal-free phthalocyanine, a β-typemetal-free phthalocyanine, a τ1-type metal-free phthalocyanine, aτ2-type metal-free phthalocyanine, and an x-type metal-freephthalocyanine.

As the metal phthalocyanine pigment, there may be used various metalphthalocyanine compounds containing a transition metal such as the metalof the Group 4A of the Periodic Table of Elements (e.g., titanium, andzirconium), the metal of the Group 5A of the Periodic Table of Elements(e.g., vanadium), the metal of the Group 3B of the Periodic Table ofElements (e.g., gallium, and indium), or the metal of the Group 4B ofthe Periodic Table of Elements (e.g., tin, and silicon). Examples of themetal phthalocyanine pigment may include oxotitanyl phthalocyanine,vanadyl phthalocyanine, hydroxygallium phthalocyanine, chlorogalliumphthalocyanine, chloroindium phthalocyanine, dichlorotin phthalocyanine,dihydroxysilicon phthalocyanine, dialkoxysilicon phthalocyanine, anddihydroxysilicon phthalocyanine dimer.

The oxotitanyl phthalocyanine may include α-type oxotitanylphthalocyanine, β-type oxotitanyl phthalocyanine, γ-type oxotitanylphthalocyanine, m-type oxotitanyl phthalocyanine, Y-type oxotitanylphthalocyanine, A-type oxotitanyl phthalocyanine, B-type oxotitanylphthalocyanine, and oxotitanyl phthalocyanine amorphous.

These phthalocyanine compounds may be prepared by a conventional method.For example, the oxotitanyl phthalocyanine may be produced in accordancewith a method described in Japanese Patent Application Laid-Open No.189873/1992 (JP-4-189873A), Japanese Patent Application Laid-Open No.43813/1993 (JP-5-43813A), or others. Moreover, the crystal structure ofthe oxotitanyl phthalocyanine may be controlled by a method such as anacid pasting or a salt milling.

The chlorogallium phthalocyanine may be, for example, produced by amethod described in Japanese Patent Application Laid-Open No. 98181/1993(JP-5-98181A). The chlorogallium phthalocyanine may be dry milled byusing a means such as an automatic mortar, a planet mill, a vibratingmill, a CF mill, a roller mill, a sand mill or a kneader, or may besubjected to wet milling with a solvent by using a means such as a ballmill, a mortar, a sand mill or a kneader after dry milling.

The hydroxygallium phthalocyanine may be prepared by a method comprisinghydrolyzing, in an acidic or alkaline solution, a chlorogalliumphthalocyanine crystal obtained by a method described in Japanese PatentApplication Laid-Open No. 263007/1993 (JP-5-263007A), Japanese PatentApplication Laid-Open No. 279591/1993 (JP-5-279591A) or others, or amethod comprising acid pasting, and others. The hydroxygalliumphthalocyanine may be subjected to wet milling with a solvent by using ameans such as a ball mill, a mortar, a sand mill or a kneader, or may betreated with a solvent after dry milling without using a solvent.

These phthalocyanine compounds may be used, by mixing or milling, as amixture obtained, or as a mixed crystal system newly formed.

The mixed crystal system may include, for example, a mixed crystal ofoxotitanyl phthalocyanine and vanadyl phthalocyanine, described inJapanese Patent Application Laid-Open No. 371962/1992 (JP-4-371962A),Japanese Patent Application Laid-Open No. 2278/1993 (JP-5-2278A),Japanese Patent Application Laid-Open No. 2279/1993 (JP-5-2279A) orothers, and a mixed crystal of oxotitanyl phthalocyanine andchloroindium phthalocyanine, described in Japanese Patent ApplicationLaid-Open No. 148917/1994 (JP-6-148917A), Japanese Patent ApplicationLaid-Open No. 145550/1994 (JP-6-145550A), Japanese Patent ApplicationLaid-Open No. 271786/1994 (JP-6-271786A), Japanese Patent ApplicationLaid-Open No. 297617/1993 (JP-5-297617A) or others.

Examples of other preferred charge-generating agent may include anazo-series pigment such as a bisazo pigment or a trisazo pigment. Amongthe azo-series pigments, a compound represented by the following formulais particularly preferred.

In the formula, R³ represents a lower alkyl group.

Incidentally, Cp¹ and Cp² in the bisazo compound, and Cp¹, Cp² and Cp³in the trisazo compound are each selected from the following groups.

In the formula, R⁴, R⁵, R⁶ and R⁷ are the same or different from eachother and each represents a hydrogen atom, a halogen atom or a loweralkyl group.

Incidentally, examples of the lower alkyl group may include a linear orbranched C₁₋₆alkyl group such as methyl, ethyl, propyl, isopropyl, butylor t-butyl group (in particular a C₁₋₄alkyl group). The halogen atomincludes a fluorine, a chlorine, a bromine or an iodine atom.

The binder resin usable for the charge-generating layer may include athermoplastic resin such as an olefinic resin (e.g., a polyethylene), avinyl-series resin (e.g., a polyvinyl chloride, a polyvinylidenechloride, a polyvinyl acetate, and a vinyl chloride-vinyl acetatecopolymer), a styrenic resin (e.g., a polystyrene), a (meth)acrylicresin [e.g., a poly(methyl methacrylate), a (meth)acrylicacid-(meth)acrylate copolymer, a (meth)acrylicacid-(meth)acrylate-(meth)acrylic acid copolymer, and a polyacrylamide],a polyamide-series resin (e.g., a polyamide 6, and a polyamide 66), apolyester-series resin (e.g., a polyalkylene arylate such as apolyethylene terephthalate or a polybutylene terephthalate, or acopolyester thereof), a polycarbonate-series resin (e.g., a bisphenolA-based polycarbonate), a polyurethane-series resin, a polyketone-seriesresin (e.g., a polyketone, and a polyvinyl ketone), a polyvinylacetal-series resin (e.g., a polyvinyl formal, and a polyvinyl butyral),or a heterocycle-containing resin (e.g., a poly-N-vinylcarbazole); athermosetting resin such as a phenol resin, a silicone resin, an epoxyresin (e.g., a bisphenol-based epoxy resin), or a vinyl ester-seriesresin such as an epoxy(meth)acrylate; and others. These binder resinsmay be used singly or in combination.

Among these binder resins, a low water-absorbing resin, for example, apolycarbonate-series resin, a polyvinyl acetal-series resin (e.g.,apolyvinyl butyral), a polyester-series resin, or the like, ispreferred.

As the polycarbonate-series resin, for example, there may be used apolycarbonate obtained by a phosgene method which comprises allowing abisphenol compound to react with phosgene; a transesterification methodwhich comprises allowing a bisphenol compound to react with a carbonicacid diester; or other method. As the bisphenol compound, for example,there may be mentioned the following compounds:

a biarenediol, for example, biphenyl-4,4′-diol, andbi-2-naphtharene-1,1′-diol,

a bis(hydroxyaryl)C₁₋₆alkane, for example, bis(4-hydroxyphenyl)methane(bisphenol F), 1,1-bis(4-hydroxyphenyl)ethane (bisphenol AD), and2,2-bis(4-hydroxyphenyl)propane (bisphenol A);

a bis(hydroxyaryl)C₁₋₆alkane having, in the arene ring thereof, at leastone substituent selected from a C₁₋₆alkyl group, a C₂₋₆alkenyl group, aC₅₋₈cycloalkyl group, a halogen atom, and the like, for example,bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane,bis(2-hydroxy-3-t-butyl-5-ethylphenyl)methane,2,2-bis(4-hydroxy-3-methylphenyl)propane (bisphenol C),2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane,2,2-bis(4-hydroxy-3-t-butylphenyl)propane,1,1-bis(4-hydroxy-3-t-butyl-6-methylphenyl)butane,2,2-bis(4-hydroxy-3-allylphenyl)propane,2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane,2,2-bis(4-hydroxy-3,5-dibromophenyl)propane,2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane,2,2-bis(4-hydroxy-3-bromophenyl)propane, and2,2-bis(4-hydroxy-3-chlorophenyl)propane;

a bisphenol compound which may have a substituent in an alkane of abis(hydroxyaryl)alkane, for example,1,1-bis(4-hydroxyphenyl)-1-phenylethane (bisphenol AP),bis(4-hydroxyphenyl)diphenylmethane, and2,2-bis(4-hydroxyphenyl)hexafluoropropane;

a ring assembly bisphenol compound, for example,1,4-bis(1-methyl-1-(4-hydroxyphenyl)ethyl)benzene, and1,3-bis(1-methyl-1-(4-hydroxyphenyl)ethyl)benzene;

a bisphenol compound having a condensed polycyclic hydrocarbon ring, forexample, 6,6′-dihydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobiindane,1,1,3-trimethyl-3-(4-hydroxyphenyl)-indan-5-ol, and6,6′-dihydroxy-4,4,4′,4′7,7′-hexamethyl-2,2′-spirobichromane;

a silicon-containing bisphenol compound, for example,α,ω-bis[3-(o-hydroxyphenyl)propyl]polydimethylsiloxane,α,ω)-bis[3-(o-hydroxyphenyl)propyl]polydimethyldiphenylsiloxane,α,ω-bis[3-(4-hydroxy-3-alkoxyphenyl)propyl]polydimethylsiloxane,α,ω-bis[2-methyl-2-(4-hydroxyphenyl)ethyl]polydimethylsiloxane,bis(4-hydroxyphenyl)dimethylsilane,bis(4-hydroxyphenyl)polydimethylsilane, andbis(4-hydroxyphenyl)polydiphenylsilane;

a bis(hydroxyaryl)C₄₋₁₀cycloalkane which may have a substituent, forexample, 1,1-bis(4-hydroxyphenyl)cyclohexane,3,3,5-trimethyl-1,1-bis(4-hydroxyphenyl)cyclohexane, and1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane;

a bis(hydroxyaryl)sulfone such as bis(4-hydroxyphenyl)sulfone,bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfoxide,bis(4-hydroxyphenyl) sulfide, bis(4-hydroxyphenyl) ketone, andbis(2-methyl-4-hydroxy-5-t-butylphenyl)sulfide;

a bisphenol compound having a heterocycle, for example,2,2′-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol],4,4′-hexamethylenediethoxycarbonylbis[2-t-butyl-6-(2H-benzotriazol-2-yl)phenol],2,2′-methylenebis[4-methyl-6-(2H-benzotriazol-2-yl)phenol]; and

triethylene glycolbis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate],3,9-bis[2-{(3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionioxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane,4-methyl-2,4-bis(4-hydroxyphenyl)-1-heptene, and a bisphenol compoundhaving a fluorene backbone.

The above-mentioned bisphenol having a fluorene backbone may include,for example, 9,9-bis(4-hydroxyphenyl)fluorene or a9,9-bis(alkylhydroxyphenyl)fluorene such as9,9-bis(4-hydroxy-3-methylphenyl)fluorene; a9,9-bis(arylhydroxyphenyl)fluorene such as9,9-bis(4-hydroxy-3-phenylphenyl)fluorene; and a9,9-bis[4-(2-hydroxy(poly)alkoxy)phenyl]fluorene such as9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene.

The proportion of the charge-generating agent may be suitably determineddepending on the species of the charge-generating agent, or the like.The proportion of the charge-generating agent is usually about 10 to1000 parts by weight, preferably about 30 to 600 parts by weight, andmore preferably about 50 to 300 parts by weight, relative to 100 partsby weight of the binder resin.

Incidentally, if necessary, the charge-generating layer may comprise theafter-mentioned charge-transporting agent.

The thickness of the charge-generating layer is, for example, about 0.01to 10 μm (e.g., about 0.01 to 5 μm), preferably about 0.05 to 2 μm, andusually about 0.1 to 5 μm.

The method for forming the charge-generating layer may be classifiedbroadly into two categories: one is a method of forming a thin coat of acharge-generating agent by a vacuum deposition method; and the other isa method of coating a liquid coating composition (solution or dispersionliquid) containing a charge-generating agent (if necessary, and a binderresin). The vacuum deposition method may include a vapor depositionmethod, a sputtering method, a reactive sputtering method, a CVD method,a glow discharge decomposition method, an ion plating method, andothers.

The above-mentioned coating method may include a conventional method,for example, a dip method, a spin coating method, a spray coatingmethod, a screen printing method, a cast method, a bar coating method, acurtain coating method, a roll coating method, a gravure coating method,a bead coating method, and others.

In the above-mentioned coating method, the liquid coating compositionmay be prepared by dissolving or dispersing the above-mentionedcharge-generating agent (and the above-mentioned binder resin) in asolvent. The solvent is not particularly limited to a specific one, andmay be selected depending on components constituting thecharge-generating layer. As the solvent, there may be mentioned aconventional solvent, for example, an ether (e.g., diethyl ether,tetrahydrofuran, and dioxane), a ketone (e.g., butanone, andcyclohexanone), an ester (e.g., methyl acetate, and ethyl acetate), ahalogenated hydrocarbon (e.g., dichloromethane, dichloroethane, andmonochlorobenzene), a hydrocarbon (e.g., hexane, toluene, and xylene),water, an alcohol (e.g., methanol, and ethanol), and others.

Incidentally, the liquid coating composition may be prepared bydispersing or mixing a charge-generating agent, a binder resin and asolvent by using a mixer (for example, a ball mill, an atritor(pulverizing mill), and a sand mill).

Moreover, after formation of a coat (charge-generating layer), the coatmay be subjected to a dry treatment. The dry treatment may be conductedunder any condition of an atmospheric pressure, an applied pressure or areduced pressure, or may be conducted at an ordinary temperature orunder heating.

(Charge-transporting Layer)

In the laminated photosensitive layer, the charge-transporting layer maycomprise a charge-transporting agent alone, and usually comprises acharge-transporting agent and a binder resin.

The charge-transporting agent may be divided broadly into two groups ofa hole transport material and an electron transport material. Thecharge-transporting agent may be used singly or in combination.

The hole transport material may include, for example, a hole transportmaterial having a low molecular weight such as an oxazole derivative, aoxadiazole derivative, a imidazole derivative, a styrylanthracene, astyrylpyrazoline, a phenylhydrazone, a triphenylmethane derivative, atriphenylamine derivative, a phenylenediamine derivative, anN-phenylcarbazole derivative, a stilbene derivative, a thiazolederivative, a triazole derivative, a phenazine derivative, an acridinederivative, a benzofuran derivative, a benzimidazole derivative, or athiophene derivative; and a hole transport material having a highmolecular weight such as a poly-N-vinylcarbazole, apolystyrylanthracene, a polyester carbonate, or a high molecular weightpolysilane (e.g., a polysilane having a number-average molecular weightof not less than 3000) such as a linear polysilane.

As the hole transport material having a low molecular weight, forexample, a diamine compound represented by the following formula (A) ispreferably used.

In the formula, R⁸ and R⁹ are the same or different from each other andeach represents a hydrogen atom, a halogen atom, a lower alkyl group, alower alkoxy group, or an aryl group; and Ar¹, Ar², Ar³ and Ar⁴ are thesame or different from each other and each represents an aryl groupwhich may have a substituent.

Incidentally, the halogen atom includes, a fluorine, a chlorine, abromine, or an iodine atom. Examples of the lower alkyl group mayinclude a linear or branched C₁₋₆alkyl group such as methyl, ethyl,propyl, isopropyl, butyl, or t-butyl group (in particular a C₁₋₄alkylgroup). The lower alkoxy group may include a linear or branchedC₁₋₆alkoxy group such as methoxy, ethoxy, propoxy, butoxy, or t-butoxygroup (in particular a C₁₋₄alkoxy group). As the aryl group, there maybe mentioned a C₆₋₁₂aryl group such as phenyl group or a naphthyl group(α-naphthyl group, β-naphthyl group), and a biphenyl group (e.g.,p-biphenyl group). The aryl group represented by R⁸ and R⁹ is oftenphenyl group. The aryl group represented by Ar¹, Ar², Ar³ and Ar⁴ may bephenyl group, a naphthyl group, a biphenyl group, and the like. Thesubstituent of the aryl group may include the halogen atom, the loweralkyl group, the lower alkoxy group, and others.

Among these diamine compounds, diamine compounds represented by thefollowing formulae (A-1), (A-2), and (A-3) are preferred.

Further, examples of the hole transport material having a low molecularweight may include a hydrazone compound represented by the followingformula (J) described in Japanese Patent Publication No. 42380/1980(JP-55-42380B), Japanese Patent Application Laid-Open No. 340999/1985(JP-60-340999A), Japanese Patent Application Laid-Open No. 23154/1986(JP-61-23154A), or others; a distyryl-series compound represented by thefollowing formula (K) described in U.S. Pat. No. 3,873,312, or others;and, in addition, a triarylamine derivative such as a triphenylmethanederivative, an N,N-diphenyl-N-biphenylamine derivative or anN,N-diphenyl-N-terphenylamine derivative,1-(p-aminophenyl)-1,4,4-triphenylbutadiene derivative described inJapanese Patent Application Laid-Open No. 288110/1999 (JP-11-288110A),other tetraphenylbutadiene-series compound, an α-phenylstilbenederivative, or a bisbutadienyltriphenylamine derivative described inJapanese Patent Application Laid-Open No. 173112/1985 (JP-7-173112A);and others. Incidentally, the usable hole transport material having alow molecular weight is not limited to these compounds.

In the formula, R¹⁰ and R¹¹ are the same or different from each otherand each represents a lower alkyl group which may have a substituent, anaryl group which may have a substituent, or an aralkyl group which mayhave a substituent; R¹² and R¹³ are the same or different from eachother and each represents a lower alkyl group which may have asubstituent, an aryl group which may have a substituent, an aralkylgroup which may have a substituent, or a heterocycle group which mayhave a substituent; R¹² and R¹³ may bond to each other to form a ring;R¹⁴ represents a hydrogen atom, a lower alkyl group which may have asubstituent, an aryl group which may have a substituent, an aralkylgroup which may have a substituent, a lower alkoxy group which may havea substituent, or a halogen atom; and R¹⁴ and R¹⁰ or R¹¹ may bond toeach other to form a ring.

In the formula, R¹⁵, R¹⁶, R¹⁷ and R¹⁸ are the same or different fromeach other and each represents a lower alkyl group, or an aryl groupwhich may have a substituent; Ar⁵ and Ar⁷ are the same or different fromeach other and each represents a phenyl group which may have as asubstituent one or more group(s) selected from the group consisting of alower alkyl group, a lower alkoxy group, an aryloxy group and a halogenatom; and Ar⁶ represents a monocyclic or polycyclic C₄₋₁₄hydrocarbonring which may have a substituent similar to that of Ar⁵ and Ar⁷ (e.g.,an aromatic hydrocarbon ring such as benzene ring), or a heterocyclewhich may have a substituent similar to that of Ar⁵ and Ar⁷.

Examples of the lower alkyl group, the lower alkoxy group, and the arylgroup may include the groups as mentioned above. As the aralkyl group,there may be mentioned a C₆₋₁₀aryl-C₁₋₄alkyl group such as benzyl group.The aryloxy group may include a C₆₋₁₀ aryloxy group such as phenoxygroup. Examples of the heterocycle group (or heterocycle) may include afive- or six-membered heterocycle group (or heterocycle) containing as aconstituent atom of the ring at least one hetero atom selected from thegroup consisting of nitrogen atom, oxygen atom and sulfur atom; and acondensed heterocycle group (or condensed heterocycle) of the five- orsix-membered heterocycle and an arene ring (e.g., benzene ring).Examples of the substituent may include a halogen atom, a C₁₋₄alkylgroup, a hydroxyl group, a C₁₋₄alkoxy group, a carboxyl group, analkoxycarbonyl group, and an acyl group. The rings formed by a linkagebetween R¹⁰ and R¹¹, a linkage between R¹² and R¹³, and a linkagebetween R¹⁴ and R¹⁰ or R¹¹ may be a three- to ten-membered ring.

The electron transport material may include, for example, a Schiff basecompound (e.g., a halogen-containing Schiff base such as chloroanyl orbromoanyl), a cyano group-containing compound (e.g., tetracyanoethylene,and tetracyanoquinodimethane), a nitro group-containing compound (e.g.,a fluorenone compound such as 2,4,7-trinitro-9-fluorenone, or2,4,5,7-tetranitro-9-fluorenone; a thioxanthone compound such as2,4,5,7-tetranitroxanthone or 2,4,8-trinitrothioxanthone; a thiophenecompound such as 2,6,8-trinitro-4H-indeno[1,2-b]thiophen-4-one or1,3,7-trinitrodibenzothiophene-5,5-dioxide), and others.

As a binder resin of the charge-transporting layer, there may be used abinder resin exemplified in the section on the charge-generating layer,or other resins. Incidentally, since the charge-transporting layer isoften formed on the charge-generating layer, among the above-exemplifiedresins, it is preferred to use, as a binder resin, a resin having a highmechanical strength or chemical stability together with a hightransparency, for example, a polycarbonate-series resin, apolyester-series resin, and others (in particular a polycarbonate-seriesresin).

The proportion of the charge-transporting agent may be suitablyselected, and for example, is about 10 to 300 parts by weight,preferably about 20 to 200 parts by weight, and more preferably about 30to 150 parts by weight relative to 100 parts by weight of the binderresin.

The thickness of the charge-transporting layer is about 3 to 100 μm,preferably about 5 to 50 μm, and more preferably about 8 to 30 μm.Moreover, in the case where the charge-transporting layer is formed froma plurality of layers, the thickness of a top surface layer thereof (orthe top surface layer of the electrophotographic photosensitive element)may be, for example, about 0.3 to 50 μm, preferably about 0.5 to 30 μm,and more preferably about 1 to 20 μm. Incidentally, the thickness of thecharge-transporting layer may be larger than that of thecharge-generating layer.

The charge-transporting layer may be formed in the same method as thecoating method described in the section on the charge-generating layer.

(Single-layered Photosensitive Layer)

The single-layered photosensitive layer contains a charge-generatingagent, a charge-transporting agent, and a binder resin in the singlelayer. Incidentally, as these components, there may be used thecharge-generating agent, the charge-transporting agent and the binderresin, mentioned above, respectively.

In the single-layered photosensitive layer, the proportion of thecharge-generating agent is about 1 to 60 parts by weight, preferablyabout 2 to 50 parts by weight, and more preferably about 3 to 40 partsby weight, relative to 100 parts by weight of the binder resin.Moreover, the proportion of the charge-transporting agent may be about30 to 150 parts by weight, preferably about 30 to 120 parts by weight,and more preferably about 30 to 100 parts by weight, relative to 100parts by weight of the binder resin.

The thickness of the single-layered photosensitive layer is usuallyabout 3 to 100 μm, preferably about 5 to 50 μm, and more preferablyabout 8 to 30 μm. Moreover, in the case where the single-layeredphotosensitive layer is formed from a plurality of layers, the thicknessof a top surface layer thereof (or the top surface layer of theelectrophotographic photosensitive element) may be, for example, about0.3 to 50 μm, preferably about 0.5 to 30 μm, and more preferably about 1to 20 μm.

The single-layered photosensitive layer may be formed by using a liquidcoating composition comprising the charge-generating agent, thecharge-transporting agent and the binder resin in the same method as thecoating method described in the section on the charge-generating layer.

Incidentally, the photosensitive layer (the single-layeredphotosensitive layer, the charge-generating layer or thecharge-transporting layer) may comprise various additives, for example,a plasticizer (e.g., a biphenyl-series compound, m-terphenyl,m-di-t-butylphenyl, and dibutylphthalate), a stabilizer (e.g., anantioxidant, and an ultraviolet ray absorbing agent), a leveling agent,a lubricant (e.g., a surface lubricant such as a silicone oil, a graftsilicone polymer, or a fluorocarbon), a potential stabilizer (e.g., adicyanovinyl compound, and a carbazole derivative), and a lightstabilizer (e.g., a hindered amine-series light stabilizer such asbis(2,2,6,6-tetramethyl-4-piperidyl) sebacate), in order to improve afilm-forming property, plasticity, coating property, durability, andothers.

(Surface Protection Layer)

The electrophotographic photosensitive element of the present inventionmay have a surface protection layer on the photosensitive layer (in thecase of the laminated photosensitive layer, the charge-generating layeror the charge-transporting layer) for protecting the surface thereofregardless of single-layered type or laminated type. The surfaceprotection layer may be a single layer or may comprise a plurality oflayers (e.g., two to five layers). Incidentally, the whole surfaceprotection layer may constitute the top surface layer. When the surfaceprotection layer comprises a plurality of layers, a layer located on thetop surface side in the protection layer may constitute the top surfacelayer.

The surface protection layer may comprise a binding agent (or a bindingcomposition) such as a binder resin (e.g., a binder resin as exemplifiedabove), a thermosetting resin (or a photo-curing resin), a hydrolyzedcondensate of a polyfunctional organic silicon compound having ahydroxyl group, a plurality of hydrolyzable groups (such as an alkoxygroup) or other groups, or the like. Moreover, the surface protectionlayer may comprise an electroconductive powder (or a mixture thereof)such as a metal oxide (tin oxide, indium oxide, indium-tin-oxide (ITO),titanium oxide) for imparting conductivity or hardness, and acharge-transporting agent (e.g., a charge-transporting agent asexemplified above), or may comprise a lubricant such as apolytetrafluoroethylene particle.

The thickness of the surface protection layer may be selected within therange that image deterioration is inhibited as much as possible. Forexample, the thickness is about 0.01 to 10 μm (e.g., about 0.01 to 5μm), preferably about 0.05 to 2 μm, and usually 0.1 to 5 μm.

The surface protection layer may be formed by coating a coatingcomposition in the same manner as the coating method described in thesection on the charge-generating layer, and then drying or hardening theresultant coat.

Incidentally, in the electrophotographic photosensitive element, when alayer (e.g., a single-layered photosensitive layer, and acharge-transporting layer) is formed by the foregoing coating method,the species of a solvent to be used is not particularly limited to aspecific one. It is preferred to use a solvent that does notsignificantly erode or dissolve a layer to be coated or an under layer(or a binder resin constituting an under layer).

As described above, in the electrophotographic photosensitive element ofthe present invention, at least the top surface layer contains apolysilane. In the top surface layer, the concentration of thepolysilane may be uniform, or may have a gradient. For example, theconcentration of the polysilane may gradually or successively declinefrom the surface side thereof. The content form of the polysilane is notparticularly limited to a specific one, and for example, includes modesas described in FIGS. 1 to 3.

FIG. 1 is a schematic sectional view of a photosensitive element forshowing an embodiment of the content form of the polysilane. In thisembodiment, the polysilane is uniformly contained in a single-layeredphotosensitive layer 2 formed on an electroconductive support 1.

FIG. 2 is a schematic sectional view of a photosensitive element forshowing another embodiment of the content form of the polysilane. Inthis embodiment, a charge-generating layer 3 and a charge-transportinglayer 4 are formed on an electroconductive support 1, and the polysilaneis uniformly contained in the charge-transporting layer 4.

FIG. 3 is a schematic sectional view of a photosensitive element forshowing still another embodiment of the content form of the polysilane.In this embodiment, a charge-generating layer 3 and acharge-transporting layer 4 are formed on an electroconductive support1, and the charge-transporting layer 4 comprises a polysilane-free layer4 a and a top surface layer 4 b uniformly containing the polysilane.

(Polysilane)

The polysilane may be a cyclic, linear, branched or mesh (or cancellous)compound having a Si—Si bond. As the polysilane, a cyclic polysilanerepresented by the above formula (1) may be usually employed.

In the above formula (1), examples of the substituent represented by theR¹ and R² may include a hydrogen atom, a hydroxyl group, an alkyl group,an alkoxy group, an alkenyl group, a cycloalkyl group, a cycloalkyloxygroup, a cycloalkenyl group, an aryl group, an aryloxy group, an aralkylgroup, an aralkyloxy group, a silyl group, and others. The substituentis often a hydrocarbon group such as an alkyl group, an alkenyl group, acycloalkyl group, an aryl group, or an aralkyl group. Moreover, thesubstituent such as a hydrogen atom, a hydroxyl group, an alkoxy groupor a silyl group is often in the terminal group of the polysilane.

The alkyl group may include a linear or branched C₁₋₁₄alkyl group suchas methyl, ethyl, propyl, isopropyl, butyl, t-butyl or pentyl(preferably a C₁₋₁₀alkyl group, and more preferably a C₁₋₆alkyl group).The alkoxy group may include a linear or branched C₁₋₁₄alkoxy group suchas methoxy, ethoxy, propoxy, isopropoxy, butoxy, t-butoxy or pentyloxy(preferably a C₁₋₁₀alkoxy group, and more preferably a C₁₋₆alkoxygroup). Examples of the alkenyl group may include a C₂₋₁₄alkenyl groupsuch as vinyl, allyl, butenyl or pentenyl (preferably a C₂₋₁₀alkenylgroup, and more preferably a C₂₋₆alkenyl group).

The cycloalkyl group may include a C₅₋₁₄cycloalkyl group such ascyclopentyl, cyclohexyl or methylcyclohexyl (preferably aC₅₋₁₀cycloalkyl group, and more preferably a C₅₋₈cycloalkyl group).Examples of the cycloalkyloxy group may include a C₅₋₁₄cycloalkyloxygroup such as cyclopentyloxy or cyclohexyloxy (preferably a C₅₋₁₀cycloalkyloxy group, and more preferably a C₅₋₈ cycloalkyloxy group).The cycloalkenyl group may include a C₅₋₁₄cycloalkenyl group such ascyclopentenyl or cyclohexenyl (preferably a C₅₋₁₀cycloalkenyl group, andmore preferably a C₅₋₈cycloalkenyl group).

The aryl group may include a C₆₋₂₀aryl group such as phenyl,methylphenyl (tolyl), dimethylphenyl (xylyl), or naphthyl (preferably aC₆₋₁₅aryl group, and more preferably a C₆₋₁₂aryl group). As the aryloxygroup, there may be mentioned a C₆₋₂₀aryloxy group such as phenoxy ornaphthyloxy (preferably a C₆₋₁₅aryloxy group, and more preferably aC₆₋₁₂aryloxy group). The aralkyl group may include a C₆₋₂₀aryl-C₁₋₄alkylgroup such as benzyl, phenethyl or phenylpropyl (preferably aC₆₋₁₀aryl-C₁₋₂alkyl group). Examples of the aralkyloxy group may includea C₆₋₂₀aryl-C₁₋₄alkyloxy group such as benzyloxy, phenethyloxy orphenylpropyloxy (preferably a C₆₋₁₀ aryl-C₁₋₂alkyloxy group).

The silyl group may include a Si₁₋₁₀silyl group such as silyl group,disilanyl group, or trisilanyl group (preferably a S₁₋₆silyl group).

Moreover, in the case where the R¹ and R² are the above-mentionedorganic substituent or silyl group, at least one hydrogen atom of theorganic substituent or silyl group may be substituted with a functionalgroup such as an alkyl group, an aryl group, or an alkoxy group. Such afunctional group may include a group similar to the foregoing group.

Among these substituents, the alkyl group (e.g., a C₁₋₄alkyl group suchas methyl group), the aryl group (e.g., a C₆₋₂₀aryl group such as phenylgroup) or other group is generally used.

In the above formula (1), at least one of the groups, R¹ and R², ispreferably an aryl group [in particular, a C₆₋₂₀aryl group (e.g., phenylgroup)]. Such a polysilane includes, for example, a cyclic polysilanewhose R¹ is an aryl group and R² is an alkyl group (in particular, acyclic polyC₆₋₂₀aryl-C₁₋₄alkylsilane such as a cyclicpolyphenylmethylsilane), a cyclic polysilane whose both R¹ and R² arearyl groups (in particular, a cyclic polyC₆₋₂₀arylsilane such as acyclic polydiphenylsilane), and the like.

The number “m” of members constituting the ring of the cyclic polysilaneis an integer of not less than 4, and is usually about 4 to 12,preferably about 4 to 10 (e.g., about 4 to 8), and more preferably about5 to 10 (e.g., about 5 to 8). The number “m” of members may be usuallyabout 5.

The cyclic polysilane may be a copolysilane (a silane-series copolymer).Such a cyclic copolysilane is, for example, represented by the followingformula (1a):

wherein R^(1a) and R^(2a) represents an aryl group which may have asubstituent; R^(1b) and R^(2b) are the same or different from each otherand each represents an alkyl group which may have a substituent, acycloalkyl group which may have a substituent, or an aryl group whichmay have a substituent; provided that both R^(1b) and R^(2b) are not anaryl group which may have a substituent coincidentally; m1 denotes aninteger of not less than 1; m2 denotes 0 or an integer of not less than1; and m1+m2 denotes an integer of not less than 4.

Examples of the aryl group represented by R^(1a), R^(2a), R^(1b) andR^(2b) may include a C₆₋₂₀aryl group similar to the R¹ and R² (e.g., aC₆₋₁₅aryl group, preferably a C₆₋₁₂aryl group, and particularly aC₆₋₁₀aryl group). The substituent of the aryl group may include an alkylgroup (a linear or branched C₁₋₁₀alkyl group such as methyl, ethyl,propyl, isopropyl, butyl, isobutyl or t-butyl group), a hydroxyl group,an alkoxy group (a linear or branched C₁₋₁₀alkoxy group such as methoxy,ethoxy, propoxy, butoxy or t-butoxy group), a carboxyl group, a linearor branched C₁₋₆alkoxy-carbonyl group, a linear or branchedC₁₋₆alkyl-carbonyl group, and others. The preferred substituent of thearyl group includes a linear or branched alkyl group (preferably aC₁₋₆alkyl group, and particularly a C₁₋₄alkyl group), or a linear orbranched alkoxy group (preferably a C₁₋₆alkoxy group, and particularly aC₁₋₄alkoxy group). The number of the substituent per the aryl group isnot particularly limited to a specific one, and may be usually selectedfrom the range of about 1 to 3. The preferred aryl group is a C₆₋₁₀arylgroup [for example, phenyl group, and a C₁₋₄ alkylphenyl group (e.g.,tolyl group, and xylyl group)], and is usually phenyl group.

Examples of the alkyl group represented by R^(1b) and R^(2b) may includea linear or branched C₁₋₁₄alkyl group similar to the above-mentioned R¹and R² (e.g., a C₁₋₁₀alkyl group, preferably a C₁₋₆alkyl group, andparticularly a C₁₋₄alkyl group). The cycloalkyl group may include aC₅₋₁₄cycloalkyl group similar to R¹ and R² mentioned above (e.g., aC₅₋₁₀cycloalkyl group, and preferably a C₅₋₈cycloalkyl group). Examplesof the substituent of the alkyl group may include a hydroxyl group, alinear or branched C₁₋₄alkoxy group, a C₅₋₈cycloalkyl group, a C₆₋₁₀arylgroup, a carboxyl group, a C₁₋₆alkoxycarbonyl group, aC₁₋₄alkyl-carbonyl group, a C₆₋₁₀aryl-carbonyl group, and others. Thesubstituent of the cycloalkyl group may include, in addition to thesubstituent of the alkyl group, a linear or branched C₁₋₄alkyl group,and others. The number of the substituent is not particularly limited toa specific one, and may be usually selected from the range of about 1 to3. The preferred R^(1b) and R^(2b) includes a C₁₋₄alkyl group (e.g.,methyl group), a C₅₋₈cycloalkyl group (e.g., cyclohexyl group), aC₆₋₁₀aryl group (e.g., phenyl group), or a C₁₋₄alkyl-C₆₋₁₀aryl group(e.g., tolyl group, and xylyl group).

Incidentally, in the cyclic copolysilane, a combination of R^(1b) andR^(2b) may be various combinations as long as both R^(1b) and R^(2b) arenot an aryl group which may have a substituent. Such a combination mayinclude, for example, (1) a combination of an alkyl group (e.g., alinear or branched C₁₋₄alkyl group) and an alkyl group (e.g., a linearor branched C₁₋₄alkyl group), (2) a combination of an alkyl group (e.g.,a linear or branched C₁₋₄alkyl group) and an aryl group (e.g., aC₆₋₁₀aryl group such as phenyl group), (3) a combination of an alkylgroup (e.g., a linear or branched C₁₋₄alkyl group) and a cycloalkylgroup (e.g., a C₅₋₈cycloalkyl group such as cyclohexyl group), or (4) acombination of an aryl group (e.g., a C₆₋₁₀aryl group such as phenylgroup) and a cycloalkyl group (e.g., a C₅₋₈ cycloalkyl group such ascyclohexyl group). The preferred combination of R^(1b) and R^(2b) is theabove-mentioned (2) or (3).

The number m1 is an integer of not less than 1 (e.g., about 1 to 10,preferably about 1 to 8, and particularly about 1 to 6), the number m2is 0 or an integer of not less than 1 (e.g., about 0 to 10, preferablyabout 0 to 8, and particular about 0 to 6). Moreover, m1+m2 is aninteger of not less than 4 (e.g., about 4 to 12, preferably about 4 to10, more preferably about 5 to 10), usually about 4 to 8 (e.g., about 5to 8), and particularly about 5.

The number-average molecular weight of the polysilane is about 200 to5000, preferably about 400 to 3000, and more preferably about 500 to2000 (e.g., about 600 to 1500). Such a polysilane is disposed to enhancedispersibility or compatibility to a resin. In such a polysilane, theratio of the weight-average molecular weight (Mw) relative to thenumber-average molecular weight (Mn) [Mw/Mn] may be about 1 to 2, andpreferably about 1.1 to 1.5.

Further, it is not necessary that the polysilane is a single compound ofthe cyclic polysilane, and the polysilane may be a polysilane mixturecontaining the cyclic polysilane. The polysilane mixture may be amixture of the cyclic polysilane (e.g., a mixture of the same series ofcyclic polysilanes different from each other in the number of members,and a mixture of different series of cyclic polysilanes), or a mixtureof the cyclic polysilane and a chain polysilane (a linear or branchedpolysilane). For example, as the polysilane, a cyclic diphenylpolysilaneand a cyclic diphenylsilane-methylphenylsilane copolymer may be used incombination. Examples of the cyclic homopolysilane may include, in theformula (1), a diarylpolysilane whose R¹ and R² are an aryl group (e.g.,a C₆₋₁₀aryl group such as phenyl group) (for example, adiphenylpolysilane), an alkylarylpolysilane whose R¹ is an alkyl group(e.g., a linear or branched C₁₋₄alkyl group) and R² is an aryl group(e.g., a C₆₋₁₀aryl group such as phenyl group), analkylcycloalkylpolysilane whose R¹ is an alkyl group (e.g., a linear orbranched C₁₋₄alkyl group) and R² is a cycloalkyl group (e.g., aC₅₋₈cycloalkyl group such as cyclohexyl group), a dialkylpolysilanewhose R¹ and R² are an alkyl group, and a dicycloalkylpolysilane whoseR¹ and R² are a cycloalkyl group (e.g., a C₅₋₈cycloalkyl group such ascyclohexyl group). Examples of the cyclic copolysilane may include adiC₆₋₁₀arylsilyl-(C₁₋₄alkyl-C₆₋₁₀aryl)silyl copolymer, adiC₆₋₁₀arylsilyl-(C₁₋₄alkyl-C₆₋₈cycloalkyl)silyl copolymer, and others.The content of the cyclic polysilane (cyclic co- or homopolysilane)represented by the formula (1) or (1a) is, relative to the totalpolysilane mixture, for example, not less than 40% by weight (e.g.,about 40 to 100% by weight), preferably not less than 50% by weight(e.g., about 50 to 100% by weight), and more preferably not less than60% by weight (e.g., about 60 to 100% by weight).

Further, the proportion of a pentameric cyclic polysilane (homo- orcopolysilane) relative to the total polysilane mixture is, for example,not less than 20% by weight (e.g., about 20 to 100% by weight),preferably not less than 30% by weight (e.g., about 30 to 90% byweight), more preferably not less than 40% by weight (e.g., about 40 to90% by weight).

(Method for Producing Polysilane)

The polysilane may be prepared by various known methods. Methods forproducing these polysilanes may include, for example, using asilicon-containing monomer having a specific structure unit as a rawmaterial, a method of condensation-polymerizing a halosilane along withdehalogenation with magnesium as a reducing agent (“magnesium reductionmethod”, e.g., WO98/29476 publication), a method ofcondensation-polymerizing a halosilane along with dehalogenation in thepresence of an alkali metal [“kipping method”, e.g., J. Am. Chem. Soc.,110, 124 (1988), and Macromolecules, 23, 3423 (1990)], a method ofcondensation-polymerizing a halosilane along with dehalogenation byelectrode reduction [e.g., J. Chem. Soc. Chem. Commun., 1161 (1990), andJ. Chem. Soc. Chem. Commun., 897 (1992)], a method ofcondensation-polymerizing a hydrazine along with dehydrogenation in thepresence of a metal catalyst (e.g., Japanese Patent ApplicationLaid-Open No. 334551/1992 (JP-4-334551A)), a method of subjecting adisilene crosslinked with a biphenyl or the like to anionicpolymerization (e.g., Macromolecules, 23, 4494 (1990)), a method ofsubjecting a cyclic silane to ring-opening polymerization, or othermethods.

Among these methods, the magnesium reduction method is the mostpreferably used in the viewpoint of the purity or molecular weightdistribution of the resulting polysilane, the excellent compatibility toa resin, the small content of sodium or chlorine, and the industrialproperty such as production cost or safety. Incidentally, water may beadded to the resulting polysilane to generate a silanol group.

Incidentally, for example, cyclization occurs during a synthetic processof the linear polysilane, as a result, the cyclic polysilane may beobtained. Moreover, the cyclic polysilane may be obtained byintramolecular cyclization of the above-mentioned polysilane, forexample, an intramolecular condensation in which both ends of thepolysilane are self-condensed. The above-mentioned intramolecularcondensation may include, for example, an intramoleculardehydrogenation, an intramolecular dehalogenation, an intramoleculardehydrohalogenation, and an intramolecular dehydration.

More specifically, the cyclic polysilane can be obtained by bringing atleast a dihalosilane, and if necessary at least one halosilane selectedfrom the group consisting of a trihalosilane, a tetrahalosilane and amonohalosilane into reaction. Examples of the halogen atom constitutingthe halosilane may include a fluorine, a chlorine, a bromine and aniodine atom, and the bromine atom or the chlorine atom (particularly thechlorine atom) is preferred.

Examples of the dihalosilane may include a compound whose R¹ and R² arean aryl group, for example, a diaryldihalosilane [e.g., adiC₆₋₁₀aryldihalosilane such as a diphenyldihalosilane, adi(C₁₋₆alkylC₆₋₁₀aryl) dihalosilane such as a ditolyldihalosilane, aC₆₋₁₀aryl-C₁₋₆alkylC₆₋₁₀aryldihalosilane such as aphenyltolyldihalosilane, and a di(C₁₋₆alkoxyC₆₋₁₀aryl) dihalosilane suchas a dimethoxyphenyldihalosilane]; a compound whose R¹ and R² are analkyl group, for example, a dialkyldihalosilane (e.g., adiC₁₋₄alkyldihalosilane such as a dimethyldihalosilane); a compoundwhose R¹ is an alkyl group and R² is a cycloalkyl group, for example, analkyl-cycloalkyldihalosilane (e.g., a C₁₋₄alkyl-C₅₋₈cycloalkyldihalosilane such as a methylcyclohexyldihalosilane); acompound whose R¹ is an alkyl group and R² is an aryl group, forexample, an alkyl-aryldihalosilane (e.g., a C₁₋₄alkyl-C₆₋₁₀aryldihalosilane such as a methylphenyldihalosilane or amethyltolyldihalosilane); and others. The preferred dihalosilaneincludes a diaryldihalosilane (e.g., a diphenyldihalosilane, and aditolyldihalosilane), an alkyl-aryldihalosilane (e.g., amethylphenyldihalosilane, and a methyltolyldihalosilane), and analkyl-cycloalkyldihalosilane (e.g., a methylcyclohexyldihalosilane).

Examples of the trihalosilane may include a C₁₋₆alkyltrihalosilane(e.g., a methyltrichlorosilane), a C₆₋₁₀cycloalkyltrihalosilane (e.g., acyclohexyltrihalosilane), and a C₆₋₁₀aryltrihalosilane (e.g., aphenyltrichlorosilane, and a tolyldichlorosilane). As themonohalosilane, there maybe mentioned, for example, atriC₁₋₆alkylhalosilane, a triC₅₋₁₀cycloalkylhalosilane, atriC₆₋₁₂arylhalosilane, a monoC₁₋₆alkyldiC₅₋₁₀cycloalkylhalosilane, amonoC₁₋₆ alkyldiC₆₋₁₂arylhalosilane, a diC₁₋₆alkylmonoC₅₋₁₀cycloalkylhalosilane, and a diC₁₋₆alkylmonoC₆₋₁₂ arylhalosilane.

These halosilanes may be used singly or in combination, respectively.Among these halosilanes, at least a dihalosilane is used in many cases,and a dihalosilane and a trihalosilane may be used in a proportion ofthe former relative to the latter of about 100/0 to 40/60 (molar ratio),and preferably about 100/0 to 50/50 (molar ratio).

Moreover, among the dihalosilanes, a diaryldihalosilane and otherdihalosilane (e.g., an alkyl-aryldihalosilane, and analkyl-cycloalkyldihalosilane) may be used in combination in a proportionof the former relative to the latter of about 100/0 to 40/60 (molarratio), and preferably about 100/0 to 50/50 (molar ratio).

The reaction of the halosilane is usually carried out in the presence ofa solvent inert to the reaction (aprotic solvent). The solvent mayinclude, for example, an ether, a carbonate, a nitrile, an amide, asulfoxide, a halogenated hydrocarbon, an aromatic hydrocarbon, analiphatic hydrocarbon, or others. These solvents may be used as a mixedsolvent.

The reaction is usually conducted in the presence of a magnesium metalcomponent. The magnesium metal component may be a magnesium metal assimple substance or a magnesium-series alloy (e.g., an alloy containingaluminum, zinc, a rare earth element, or others), a mixture containingthe magnesium metal or alloy, and others.

Examples of the shape (or form) of the magnesium metal component mayinclude a particulate form (e.g., a powder, and a granule), aribbon-shaped form, a cut or shaved piece, a massive form, a rod-likeform, and a plate form. In particular, a shape (or form) having a largesurface area (e.g., a powder, a granule, a ribbon-shaped form, and a cutor shaved piece) is preferred. In the case where the magnesium metalcomponent is a particulate form, the average particle size thereof isabout 1 to 10000 μm, preferably about 10 to 5000 μm, and more preferablyabout 20 to 1000 μm.

The amount to be used of the magnesium metal component is usually, interms of magnesium, about 1 to 20 equivalent, preferably about 1.1 to 14equivalent, and more preferably 1.2 to 10 equivalent (e.g., about 1.2 to5 equivalent), relative to the halogen constituting the halosilane.Moreover, the amount (mol) to be used of the magnesium metal componentis usually, as magnesium, about 1 to 20 time(s), preferably about 1.1 to14 times, and more preferably about 1.2 to 10 times (e.g., about 1.2 to5 times) as large as that of the halosilane.

It is sufficient that the reaction is carried out in the presence of atleast the magnesium metal component. In order to acceleratepolymerization of the halosilane, it is advantageous that the reactionis conducted in the coexistence of the magnesium metal component and atleast one member selected from the group consisting of a lithiumcompound and a metal halide, in particular in the coexistence of themagnesium metal component and both of a lithium compound and a metalhalide.

As the lithium compound, there may be used a lithium halide (e.g.,lithium chloride, lithium bromide, and lithium iodide), a salt of aninorganic acid (e.g., lithium nitrate, lithium carbonate, lithiumhydrogen carbonate, lithium sulfate, lithium perchlorate, and lithiumphosphate) and others. The preferred lithium compound includes a lithiumhalide (particularly lithium chloride). The proportion of the lithiumcompound is, relative to 100 parts by weight of the total amount of thehalosilane(s), about 0.1 to 200 parts by weight, preferably about 1 to150 parts by weight, more preferably about 5 to 100 parts by weight(e.g., about 5 to 75 parts by weight) and usually about 10 to 80 partsby weight.

Examples of the metal halide may include a polyvalent metal halide suchas a halide (e.g., a chloride, a bromide, and an iodide) of a metal, forexample, a transition metal (e.g., the metal of the Group 3A of thePeriodic Table of Elements such as samarium, the metal of the Group 4Aof the Periodic Table of Elements such as titanium, the metal of theGroup 5A of the Periodic Table of Elements such as vanadium, the metalof the Group 8 of the Periodic Table of Elements such as iron, nickel,cobalt or palladium, the metal of the Group 1B of the Periodic Table ofElements such as copper, and the metal of the Group 2B of the PeriodicTable of Elements such as zinc), the metal of the Group 3B of thePeriodic Table of Elements (e.g., aluminum), or the metal of the Group4B of the Periodic Table of Elements (e.g., tin). The valence of themetal constituting the metal halide is preferably 2 to 4, andparticularly 2 or 3. The proportion of the metal halide is, relative to100 parts by weight of the total amount of the halosilane(s), about 0.1to 50 parts by weight, preferably about 1 to 30 parts by weight, andmore preferably about 2 to 20 parts by weight.

The reaction may be conducted by putting a reaction component, amagnesium metal component and a solvent, and if necessary a lithiumcompound and/or a metal halide in an airtight reaction vessel, andstirring the mixture. The inside of the reaction vessel may be in a dryatmosphere, and is preferably in a dry atmosphere of an inactive gas(e.g., a nitrogen gas, a helium gas, and an argon gas). The reactiontemperature is usually within the range from −20° C. to a boiling pointof the solvent, preferably from about 0 to 80° C., and more preferablyfrom about 20 to 70° C. The resulting polysilane may be purified by aconventional method, for example, a reprecipitation method using a goodsolvent and a poor solvent, an extraction method, and others.

Such a polysilane has a high affinity or compatibility to a resin (e.g.,a polycarbonate-series resin), and even a small amount of the polysilaneimparts a high water repellency and lubricating property (lubricity) tothe resin. Moreover, dispersibility to a resin is high, for example in acoat layer, the polysilane can be uniformly dispersed in the thicknessdirection (in-depth) of the layer without segregation. Therefore,addition of the polysilane in at least the top surface layer of thephotosensitive layer realizes conservation of a lubricity or cleaningproperty of the photosensitive layer at a high level without causingbleeding out even when the top surface layer part is worn away byfriction or sliding. Moreover, a high transparency of the photosensitivelayer (in particular a photosensitive layer containing a resin binder)realizes a high definition image in an electrophotographicphotosensitive element, and keeps up a high quality and high definitionimage property for a long period without causing deterioration indefinition (or fineness), such as blur of printed character. Further, asmall amount to be added of the polysilane does not deteriorate amechanical strength of the photosensitive element (in particular thephotosensitive layer), if anything, enhances or improves a mechanicalstrength of the photosensitive element.

(Proportion of Polysilane)

The polysilane may be contained in at least the top surface layer of theelectrophotographic photosensitive element. According to the presentinvention, even when the content of the polysilane is small, a highlubricity or cleaning property can be realized.

Incidentally, in the photosensitive element of the present invention,addition of a small amount of the polysilane to the photosensitive layer(or the top surface layer of the photosensitive layer) can improve orenhance a mechanical strength of the photosensitive element (or thephotosensitive layer), and can improve abrasion resistance. Therefore,the surface protection layer is not necessarily provided.

The content of the polysilane may be selected from the range in whichwater repellency or lubricity, and transparency are not deteriorated,and may be about 0.01 to 10% by weight, preferably about 0.05 to 5% byweight, and more preferably about 0.08 to 3% by weight (e.g., about 0.1to 2% by weight) relative to the whole components of the top surfacelayer. The proportion of the polysilane is often about 0.01 to 5% byweight relative to the whole components of the top surface layer, andeven when the proportion of the polysilane is about 0.01 to 3% by weight(e.g., about 0.1 to 1.5% by weight, and particularly about 0.25 to 1.5%by weight) relative to the whole components of the top surface layer,the properties (or characteristics) of the photosensitive layer can besignificantly improved. In order to reduce the amount to be used of thepolysilane, a cyclic homo- or copolysilane having at least adiarylsilane unit (e.g., a diarylpolysilane, and adiaryldihalosilane-alkylaryldihalosilane copolymer) is advantageous.

Incidentally, in the case where the top surface layer comprises a binderresin, the proportion of the polysilane may be, for example, about 0.01to 15 parts by weight (e.g., about 0.02 to 10 parts by weight),preferably about 0.05 to 8 parts by weight, and more preferably about0.1 to 5 parts by weight (e.g., about 0.1 to 3 parts by weight),relative to 100 parts by weight of the binder resin.

Moreover, in the case where the top surface layer comprises thecharge-transporting agent and/or the charge-generating agent(particularly the charge-transporting agent), the proportion of thepolysilane may be about 0.01 to 20 parts by weight, preferably about0.05 to 15 parts by weight, and more preferably about 0.1 to 10 parts byweight (e.g., about 0.1 to 5 parts by weight) relative to 100 parts byweight of the charge-transporting agent or charge-generating agent.

The method for allowing the photosensitive element to contain thepolysilane is not particularly limited to specific one, and variousmethods are available. For example, in the case where the top surfacelayer is formed by coating a liquid coating composition, the polysilanemay be added to a solvent together with other components (e.g., a binderresin, a charge-transporting agent, a charge-generating agent, and abinding agent) in preparation of the liquid coating composition, or maybe precedently melt-kneaded with a binder resin in the preparation of abinder resin pellet.

The composition containing the polysilane significantly improvesabrasion resistance, durability, and other properties of thephotosensitive layer without deteriorating an electrostatic property,photosensitivity, and others. The present invention therefore includesan electrophotographic photosensitive element composition comprising acomponent for the outer surface layer of the photosensitive layer or acomponent for the surface protection layer of the photosensitive layer,and a cyclic polysilane. This composition may be, for example, preparedby mixing components constituting the single-layered photosensitivelayer, the charge-generating layer, the charge-transporting layer or thesurface protection layer. The composition may be a liquid coatingcomposition or coating composition containing an organic solvent. Thecomposition usually comprises at least one member selected from thegroup consisting of the charge-generating agent and thecharge-transporting agent, a binder (e.g., a polycarbonate-seriesresin), and a cyclic polysilane, depending on the structure of thephotosensitive layer, or others.

Moreover, the electrophotographic photosensitive element of the presentinvention can be produced by forming at least a photosensitive layer onan electroconductive support, and at least the top surface layer (e.g.,a charge-transporting layer) of the photosensitive layer may comprise apolysilane. The method for forming a photosensitive layer on anelectroconductive support is not particularly limited to a specific one,and may be a conventional method (e.g., a method of coating theforegoing liquid coating composition). For example, in the case of alaminated photosensitive layer of which the top surface layer is acharge-transporting layer, the electrophotographic photosensitiveelement may be formed by coating a liquid coating composition containinga charge-generating agent on an electroconductive support (or chargeinjection-blocking layer), and further coating a liquid coatingcomposition containing a charge-transporting agent (and a polysilane)thereon. Moreover, in the case where the functional layer (e.g., thecharge-transporting layer) comprises a plurality of layers, for example,coating compositions different from each other in concentration (e.g.,including a combination of a polysilane-free liquid coating compositionand a liquid coating composition containing a polysilane) maysequentially coated to form the functional layer.

[Electrophotographic Apparatus]

The electrophotographic photosensitive element of the present inventionmay be used as a constituent unit of an electrophotographic apparatus.The electrophotographic apparatus is provided with constituent unitssuch as the foregoing electrophotographic photosensitive element, acharging means, an exposing means (aligner), a developing means, atransferring means, a cleaning means, and a fixing means.

FIG. 4 is a schematic sectional view for showing an embodiment of anelectrophotographic apparatus provided with the electrophotographicphotosensitive element of the present invention. In FIG. 4, a rotatableelectrophotographic photosensitive element 41 having a circular cylinderconfiguration in cross section is positively or negatively charged in asurface thereof by means of a charging means (charging unit) 42 equippedwith a charging instrument (e.g., a corona discharging instrument), issubjected to exposure to a light of a light image by a light-exposingmeans (exposing unit) 43 equipped with a light source, thereby anelectrostatic latent image corresponding to the light image on thesurface of the photosensitive element is formed. The electrostaticlatent image is developed by a toner of a developing means (developingunit) 44 equipped with a developing instrument, and a toner on thesurface of the photosensitive element is transferred to an object 46(such as a paper) by a transferring means (transferring unit) 45equipped with a charging means. The object 46 on which the toner istransferred is fixed by a fixing means (not shown) to obtain a printedmatter. The residual toner on the surface of the photosensitive element41 after transferring is removed by a cleaning means (cleaning unit) 47equipped with a cleaning blade, and charges on the surface is eliminatedby the exposing means 43. Thereby the process is completed.

Incidentally, the configuration (or form) of the electrophotographicphotosensitive element may be selected depending on the configuration(or form) of the electroconductive support without particularlimitation, e.g., may be in the form of a dram (or a roll or cylinder)as shown in the Fig., or may be a flat form such as a belt (or a sheet).

Examples of the charging instrument usable in the charging means or thetransferring means may include a conventional charging instrument, e.g.,a corotron, a scorotron, a solid charging instrument, and a chargingroller. Incidentally, in the transferring means, a plurality oftransferring means, for example a transferring charger and a separatingcharger, may be used in combination.

The exposure wavelength of the light source in the exposure means is notparticularly limited to a specific one, and for example, is about 100 to1000 nm, preferably about 200 to 900 nm, and more preferably about 300to 800 nm.

Moreover, the light source of the exposure means may be selectedaccording to the sensitizing wavelength of the photosensitive elementwithout limitation to a specific one. The light source may include afluorescent lamp, a tungsten lamp, a halogen lamp, a mercury lamp, asodium lamp, a light emitting diode (LED), a laser [for example, a laserdiode (LD), an excimer laser (e.g., XeCl (308 nm), KrF (248 nm), KrCl(222 nm), ArF (193 nm), ArCl (172 nm), and F₂ (157 nm))], anelectroluminescence (EL), and others. Incidentally, the exposure meansmay be equipped with a filter or the like in order to tune (or adjust)the wavelength of the light source.

As the toner of the development unit, there may be used a toner obtainedby a powdering method, a toner obtained by a suspension polymerizationmethod, or others. The toner may be a black toner, and a color toner(e.g., a yellow toner, a red toner, or a blue toner).

In the cleaning means, a cleaning method is not particularly limited toa specific one, and may be a blade cleaning method using a cleaningblade as shown in the Figure, a brush cleaning method using a cleaningbrush (such as a fur brush or a magnetic fur brush), or a combinationmethod thereof.

According to the present invention, water repellency and lubricity inthe electrophotographic photosensitive element can be improved and animage having a high quality over a long term can be formed. Moreover,even in the case of wearing a surface layer of the electrophotographicphotosensitive element, durability can be significantly improved withoutdeterioration in a property such as a lubricating property or a cleaningproperty. Further, the electrophotographic photosensitive elementrealizes a high definition image without deterioration in a mechanicalproperty or transparency, and ensures conservation of a high-qualityimage property even with prolonged application.

INDUSTRIAL APPLICABILITY

The electrophotographic photosensitive element and electrophotographicapparatus of the present invention is available for a variety ofapparatus, e.g., various image-forming apparatuses such as a copyingmachine, a facsimile, and a printer (e.g., a laser printer). Theseimage-forming apparatuses may be capable of forming a color image. Thephoto sensitive element may be fixed and mounted on these apparatuses,or mounted thereon in the form of an exchangeable cartridge.

EXAMPLES

The following examples are intended to describe this invention infurther detail and should by no means be interpreted as defining thescope of the invention. Incidentally, the term “part(s)” indicates thepart(s) by weight in EXAMPLES.

Example 1

(Preparation of Liquid Coating Composition for Charge-generating Layer)

One part of a Y-type TiOPc (oxotitanyl phthalocyanine, manufactured bySanyo Color Works, Ltd.), 0.8 part of a polyvinylbutyral resin (tradename: S-LEC BM-S, manufactured by Sekisui Chemical Co., Ltd.), and 50parts of cyclohexanone were mixed, and subjected to ball mill dispersionwith zirconia beads for 24 hours to obtain a liquid coating compositionfor a charge-generating layer.

(Preparation of Liquid Coating Composition for Charge-transportingLayer)

Ten parts of a bisphenol Z-based polycarbonate (trade name “Iupilon”,manufactured by Mitsubishi Gas Chemical Company, Inc.) as a binder, 10parts of N,N′-diphenyl-N,N′-di(m-tolyl)-p-benzidine (TPD) as acharge-transporting agent, 0.2 part of decaphenylcyclosilane(five-membered ring, hereinafter represented by “PDPS”), and 42 parts ofmonocyclobenzene and 18 parts of dichloromethane as solvents were mixed,and subjected to dispersion with a roller mill for 24 hours to obtain aliquid coating composition for a charge-transporting layer.

Incidentally, “PDPS” was prepared as follows.

That is, to a round flask (internal volume: 1000 ml) equipped with athree-way stopcock, 30.0 g of granular magnesium (particle size: 20 to1000 μm), 40.0 g of anhydrous lithium chloride (LiCl) and 20.0 g ofanhydrous iron chloride (II) (FeCl₂) were fed, and driedwithheating at50° C. under a reduced pressure of 1 mmHg (=133 kPa). Thereafter, dryargon gas was introduced into the reaction vessel, 500 ml oftetrahydrofuran pre-dried with sodium-benzophenone ketyl was addedthereto, and stirred for about 30 minutes at a room temperature.Diphenyldichlorosilane (30 g) purified by distillation was added to themixture by a dropping funnel, and the resulting mixture was stirred at50° C. for about 24 hours. After completion of the reaction, 250 ml of1N (=1 mol/L) hydrochloric acid was put in the reaction mixture, and thereaction mixture was subjected to extraction with 1000 ml of toluene.The toluene layer was washed in three steps with 200 ml aliquots ofpurified water, and was dried with anhydrous magnesium sulphate, thentoluene was removed to give a cyclic polydiphenylsilane (5-memberedring) as a white powder (molecular weight based on mass spectrum (MS):910, yield: 70%).

(Evaluations of Water Repellency and Silicon Component Dispersibility)

An aluminum sheet having a thickness of 50 μm was used as a substrate,and a liquid coating composition for a charge-transporting layer wascoated on the substrate by a bar coating method using a wire bar (No.50), and dried at 120° C. for 60 minutes to give a thin layer of acharge-transporting layer having a thickness of 15 μm. Concerning theobtained thin layer, the contact angle of water was measured.

Moreover, the charge-transporting layer was separated from the aluminumsheet substrate, then filled in an epoxy resin, and the epoxy resin iscured. The resulting matter was polished by using an emery paper so thatthe cross section of the charge-transporting layer appeared. In order toimpart conductivity to the matter, gold (Au) was deposited at athickness of 100 nm on the polished surface by using a sputtering methodto give a sample for chemical composition analysis. Regarding the crosssection of the obtained sample, the chemical composition analysis wasconducted by using an electron probemicroanalysis (EPMA) method(analyzer: “JXA-8900RL”, manufactured by JEOL, Ltd.). From thedistribution results, the uniform dispersibility of the siliconcomponent to the cross section of the coat was evaluated. FIG. 5 is afigure showing a result of analysis of a composition distribution in thecross section of the charge-transporting layer. In FIG. 5, the whiteparts on both sides in the thickness direction are an epoxy resin 51,and the central part is a charge-transporting layer 52. As apparent fromFIG. 5, the polysilane was uniformly dispersed in thecharge-transporting layer 52.

In the upper right hand corner of FIG. 5, a shaded bar with thecorresponding level and degree of the relative distribution of Silicon(Si) and Gold (Au) is shown for use in interpreting FIG. 5.

(Printing Test)

An aluminum tube (conductive support) having an external diameter of 30mm was dipped in a methyl alcohol solution containing a nylon resin(trade name “Amilan CM8000”, manufactured by Toray Industries, Inc.)mixed in a proportion of 5% by weight, and dried at 80° C. for 20minutes to form an undercoat layer having a thickness of 0.8 μm. Then,the liquid coating composition for a charge-generating layer was dippedon this undercoat layer, and dried at 80° C. for 10 minutes to form acharge-generating layer having a thickness of 0.3 μm. Further, theliquid coating composition for a charge-transporting layer was dipped onthis charge-generating layer, and dried at 120° C. for 60 minutes toform a charge-transporting layer having a thickness of 22 μm, and adrum-like electrophotographic photosensitive element was produced.

The obtained electrophotographic photosensitive element was loaded in atesting machine obtained by making alterations to a commerciallyavailable laser printer equipped with an electrophotographic apparatussimilar to FIG. 4 mentioned above, and the printing image was evaluatedwith the testing machine after actually printing. Incidentally, in thelaser printer, the charging means 42 comprises a corona charginginstrument, and the light-exposing means 43 comprises a laser diode(wavelength: 780 nm). The image evaluation was based on a test patternhaving solid and thin line parts, and an initial printed image obtainedby printing the test pattern and an printed image obtained afterprinting 20000 sheets of the test pattern were visually determined.Moreover, the decreased thickness (abrasion loss) of the photosensitiveelement after printing 20000 sheets of the test pattern was measured.

Example 2

A photosensitive element was made in the same manner as Example 1 exceptthat the amount of PDPS in the liquid coating composition for acharge-transporting layer was 0.5 part instead of 0.2 part, and wasevaluated similar to Example 1.

Comparative Example 1

A photosensitive element was made in the same manner as Example 1 exceptthat the liquid coating composition for a charge-transporting layer wasprepared without adding PDPS, and was evaluated similar to Example 1.

Comparative Example 2

A photosensitive element was made in the same manner as Example 1 exceptthat 0.1 part of methylphenylsilicone (“KF56”, manufactured by Shin-EtsuSilicones) was used instead of 0.2 part of PDPS in the liquid coatingcomposition for a charge-transporting layer in Example 1, and wasevaluated similar to Example 1.

Comparative Example 3

A photosensitive element was made in the same manner as Example 1 exceptthat 0.2 part of methylphenylsilicone (“KF56”, manufactured by Shin-EtsuSilicones) was used instead of 0.2 part of PDPS in the liquid coatingcomposition for a charge transfer layer in Example 1, and was evaluatedsimilar to Example 1.

Comparative Example 4

A photosensitive element was made in the same manner as Example 1 exceptthat 2.5 parts of a linear poly(methylphenylsilane) (PMPS,number-average molecular weight of 12000, weight-average molecularweight of 23000) was used instead of 0.2 part of PDPS in the liquidcoating composition for a charge-transporting layer in Example 1, andwas evaluated similar to Example 1.

Incidentally, PMPS was prepared as follows.

To a round flask (internal volume: 1000 ml) equipped with a three-waystopcock, 60.0 g of granular magnesium (particle size: 20 to 1000 μm),16.0 g of anhydrous lithium chloride (LiCl) and 9.6 g of anhydrous ironchloride (II) (FeCl₂) were fed, and the mixture was dried with heatingat 50° C. under a reduced pressure of 1 mmHg (=133 kPa). Thereafter, dryargon gas was introduced into the reaction vessel, 540 ml oftetrahydrofuran pre-dried with sodium-benzophenone ketyl was addedthereto, and stirred for about 30 minutes at a room temperature.Sixty-four (64) ml of methylphenyldichlorosilane purified bydistillation was added to the mixture by a syringe, and the resultingmixture was stirred at a room temperature for about 12 hours. Aftercompletion of the reaction, 500 ml of 1N hydrochloric acid was put inthe reaction mixture, and the reaction mixture was subjected toextraction with 1000 ml of diethyl ether. The ether layer was washed intwo steps with 500 ml aliquots of purified water, and was dried withanhydrous magnesium sulphate, and then ether was removed to give a crudepolysilane containing a low molecular weight by-product. The crudepolysilane was reprecipitated with 200 ml of tetrahydrofuran as a goodsolvent and 4000 ml of ethanol as a poor solvent to obtain a PMPS[number-average molecular weight of 12000, weight-average molecularweight of 23000, and yield of 85%, in accordance with gel-permeationchromatography (GPC) (in terms of polystyrene)].

The results were shown in Table 1. Incidentally, in Table 1, “A”represents the cyclic PDPS, “B” represents the methylphenylsilicone, “C”represents the linear PMPS, and the dispersibility of the siliconcomponent (the cyclic polysilane, the linear polysilane, the silicone)and the image were evaluated as follows.

Dispersibility of Silicon Component

“A”: the silicon component is uniformly dispersed in the whole crosssection of the coat.

“B”: the silicon component is unevenly distributed in the form of anislands-in-an ocean structure.

“C”: the silicon component is unevenly distributed in the top surfacelayer.

Evaluation of image

“A”: good

“B” to “C”: blur of image and fog occur.

TABLE 1 Evaluation of Dispersibility image Amount Contact angle ofsilicon After 20000 Abrasion Additive (part) (°) component TransparencyInitial printing loss (μm) Ex. 1 A 0.2 85 A Good A A 1.5 Ex. 2 A 0.5 86A Good A A 1.4 Com. Ex. 1 none 0 76 — Good A C 5.6 Com. Ex. 2 B 0.1 85 Cslightly B C 4.1 clouded Com. Ex. 3 B 0.2 85 C slightly B C 3.8 cloudedCom. Ex. 4 C 2.5 87 B clouded C C 6.6

As apparent from Table 1, in Examples, even when the amount to be usedof the silicon component was small compared with Comparative Examples,the photosensitive element could highly improve the water repellency anddurability without deteriorating the transparency. In addition, an imagewas printed without deteriorating the image quality even in the case ofusing over a long period.

Example 3

A photosensitive element was made in the same manner as Example 1 exceptthat 0.1 part of PDPS was used instead of 0.2 part of PDPS in the liquidcoating composition for a charge transfer layer, and was evaluatedsimilar to Example 1.

Example 4

A photosensitive element was made in the same manner as Example 1 exceptthat 0.15 part of PDPS was used instead of 0.2 part of PDPS in theliquid coating composition for a charge transfer layer, and wasevaluated similar to Example 1.

Example 5

A photosensitive element was made in the same manner as Example 1 exceptthat 0.15 part of PDPS was used instead of 0.2 part of PDPS in theliquid coating composition for a charge transfer layer and that 7 partsof TPD was used instead of 10 parts of TPD in the charge-transportingagent, and was evaluated similar to Example 1.

Example 6

A photosensitive element was made in the same manner as in Example 1except that 0.2 part of a cyclic diphenylsilane-methylphenylsilanecopolymer (PDPMPS) was used instead of 0.2 part of PDPS in the liquidcoating composition for a charge transfer layer, and was evaluatedsimilar to Example 1.

Incidentally, the cyclic PDPMPS was prepared as follows.

That is, to a round flask (internal volume: 1000 ml) equipped with athree-way stopcock, 30.0 g of granular magnesium (particle size: 20 to1000 μm), 40.0 g of anhydrous lithium chloride (LiCl) and 20.0 g ofanhydrous iron chloride (II) (FeCl₂) were fed, and the mixture was driedwith heating at 50° C. under a reduced pressure of 1 mmHg (=133 kPa).Thereafter, dry argon gas was introduced into the reaction vessel, 500ml of tetrahydrofuran pre-dried with sodium-benzophenone ketyl was addedthereto, and stirred for about 30 minutes at a room temperature. Amixture of diphenyldichlorosilane (30.4 g (0.12 mol)) purified bydistillation and methylphenyldichlorosilane (5.7 g (0.03 mol)) purifiedby distillation were added thereto by a dropping funnel, and theresulting mixture was stirred at 50° C. for about 24 hours. Aftercompletion of the reaction, 250 ml of 1N (=1 mol/L) hydrochloric acidwas put in the reaction mixture, and the reaction mixture was subjectedto extraction with 1000 ml of toluene. The toluene layer was washed inthree steps with 200 ml aliquots of purified water, and dried withanhydrous magnesium sulphate, then toluene was removed to give a mixtureof a cyclic polydiphenylsilane (5-membered ring) and a cyclicdiphenyldichlorosilane-methylphenyldichlorosilane copolymer (4- to6-membered ring) as a white solid [number-average molecular weight of950, weight-average molecular weight of 1020 and yield of 85%, inaccordance with gel-permeation chromatography (GPC) (conversion in termsof polystyrene)].

Example 7

Except for using a bisphenol A-based polycarbonate (trade name: “IupilonE-2000”, manufactured by Mitsubishi Gas Chemical Company, Inc.) insteadof the bisphenol Z-based polycarbonate and using dichloromethane insteadof monochlorobenzene as a solvent, an operation was conducted in thesame manner as Example 1.

Example 8

An operation was conducted in the same manner as Example 1 except that acopolycarbonate of biphenol and bisphenol A (trade name “Tough Z”,manufactured by Idemitsu Kosan Co., Ltd.) was used instead of thebisphenol Z-based polycarbonate.

Example 9

An operation was conducted in the same manner as Example 1 except that acopolycarbonate of 9,9-bis(4-hydroxy-3-methylphenyl)fluorene andbisphenol A prepared in accordance with Example 1 of Japanese PatentApplication Laid-Open No. 134198/1996 (JP-8-134198A) was used instead ofthe bisphenol Z-based polycarbonate.

Comparative Example 5

A photosensitive element was made in the same manner as Example 1 exceptthat 0.2 part of a linear poly(diphenylsilane) PDPS (number-averagemolecular weight: 2200, weight-average molecular weight: 3400) was usedinstead of 0.2 part of PDPS in the liquid coating composition for acharge transfer layer, and was evaluated similar to Example 1.

Incidentally, the linear PDPS was prepared as follows.

A stirrer, a Dimroth condenser, a thermometer, and a 100 ml droppingfunnel were installed in a four-neck round flask (internal volume: 1000ml). Dry argon gas was passed through the flask, and the flask wasallowed to stand overnight. In the flask, 24.0 g of metallic sodium and350 ml of dry toluene were charged, and boiled up in an oil bath. On theother hand, 90.0 g of diphenyldichlorosilane was fed in the droppingfunnel, and gradually dropped over 40 minutes. After completion of thedropping, the mixture was kept boiling for another 2 hours, and cooleddown to complete the reaction. Thereafter, 100 ml of methanol wasgradually dropped in the mixture to consume the remaining metallicsodium. Then the reaction mixture was transferred to a separatingfunnel, and the by-product sodium chloride was repeatedly extracted fromthe mixture with 200 ml of water. The organic layer was dried withanhydrous magnesium sulphate, and then the solvent was removed to give48 g of a crude polysilane.

The crude polysilane was dissolved in 200 ml of tetrahydrofuran, and 500ml of acetone was gently added thereto with stirring to reprecipitatethe polysilane. The precipitate was separated by filtration, and driedto give a linear polydiphenylsilane.

TABLE 2 Image After Amount Contact angle 20000 Abrasion Additive (part)(°) Dispersibility Transparency Initial printing loss (μm) Ex. 3 A 0.183 A Good A A 1.7 Ex. 4 A 0.15 85 A Good A A 1.5 Ex. 5 A 0.15 86 A GoodA A 1.3 Ex. 6 D 0.2 85 A Good A A 1.6 Ex. 7 A 0.2 84 A Good A A 3.3 Ex.8 A 0.2 85 A Good A A 2.1 Ex. 9 A 0.2 85 A Good A A 1.9 Com. Ex. 5 E 0.279 B generation of C C 5.5 particles

Incidentally, in Example 5, 7 parts of TPD was used. In the column of“Additive” in Tables, “A” represents the 5-membered cyclic PDPS, “D”represents the cyclic diphenylsilane-methylphenylsilane copolymer, and“E” represents the linear PDPS.

1. An electrophotographic photosensitive element comprising at least atop surface layer containing a polysilane, wherein the polysilanecomprises a cyclic polysilane represented by the following formula (1):

wherein R¹ and R² are the same or different from each other and eachrepresents an alkyl group, a cycloalkyl group, an aryl group, or anaralkyl group, at least one hydrogen atom of the alkyl group, thecycloalkyl group, the aryl group, or the aralkyl group, may besubstituted with an alkyl group, a cycloalkyl group, an aryl group, oran aralkyl group; “m” denotes an integer of not less than 4; and R¹ andR² may vary depending on the coefficient “m”, respectively.
 2. Anelectrophotographic photosensitive element according to claim 1,wherein, in the formula (1), at least one of R¹ and R² represents anaryl group, and “m” is an integer of 4 to
 10. 3. An electrophotographicphotosensitive element according to claim 1, wherein, in the formula(1), R¹ and R² each represents a phenyl group, and “m” is an integer of4 to
 8. 4. An electrophotographic photosensitive element according toclaim 1, wherein the cyclic polysilane is represented by the followingformula (1a):

wherein R^(1a) and R^(2a) each represents an aryl group in which atleast one hydrogen atom thereof may be substituted with an alkyl group;R^(1b) and R^(2b) are the same or different from each other and eachrepresents an alkyl group which at least one hydrogen atom thereof maybe substituted with a C₅₋₈cycloalkyl group or a C₆₋₁₀aryl group, acycloalkyl group in which at least one hydrogen atom thereof may besubstituted with a linear or branched C₁₋₄alkyl group, a C₅₋₈cycloalkylgroup or a C₆₋₁₀aryl group, or an aryl group in which at least onehydrogen atom thereof may be substituted with an alkyl group; providedthat both R^(1b) and R^(2b) are not coincidentally an aryl group inwhich at least one hydrogen atom thereof may be substituted with analkyl group; m1 denotes an integer of not less than 1; m2 denotes 0 oran integer of not less than 1; and m1+m2 denotes an integer of not lessthan
 4. 5. An electrophotographic photosensitive element according toclaim 4, wherein R^(1a) and R^(2a) each represents a C₆₋₁₀aryl group; acombination of R^(1b) and R^(2b) is (1) a combination of a C₁₋₄alkylgroup and a C₁₋₄alkyl group, (2) a combination of a C₁₋₄alkyl group anda C₆₋₁₀aryl group, (3) a combination of a C₁₋₄alkyl group and aC₅₋₈cycloalkyl group, or (4) a combination of a C₆₋₁₀aryl group and aC₅₋₈cycloalkyl group.
 6. An electrophotographic photosensitive elementaccording to claim 4, wherein m1 is an integer of 1 to 10, m2 is aninteger of 0 to 10, and m1+m2 is 4 to
 12. 7. An electrophotographicphotosensitive element according to claim 4, wherein m1 is an integer of1 to 8, m2 is an integer of 0 to 8, and m1+m2 is 4 to
 10. 8. Anelectrophotographic photosensitive element according to claim 1, whereinthe polysilane is a polysilane mixture containing a cyclic polysilane.9. An electrophotographic photosensitive element according to claim 8,wherein the top surface layer comprises an outer surface layer of thephotosensitive layer or a surface protection layer of the photosensitivelayer, and the proportion of a cyclic homo- or copolysilane having atleast a diarylsilane unit is 0.01 to 3% by weight relative to wholecomponents of the top surface layer.
 10. An electrophotographicphotosensitive element according to claim 1, which comprises at leastboth of an electroconductive support and a photosensitive layer, whereinthe photosensitive layer comprises at least the following components: acharge-generating agent; a charge-transporting agent; and a binderresin.
 11. An electrophotographic photosensitive element according toclaim 10, wherein the photosensitive layer comprises a charge-generatinglayer, and a charge-transporting layer formed on the charge-generatinglayer.
 12. An electrophotographic photosensitive element according toclaim 10, wherein a surface protection layer containing the polysilaneis formed on the photosensitive layer.
 13. An electrophotographicphotosensitive element according to claim 1, wherein the content of thecyclic polysilane is 0.01 to 10% by weight relative to the wholecomponents of the top surface layer.
 14. An electrophotographicphotosensitive element according to claim 1, wherein the content of thecyclic polysilane is 0.01 to 5% by weight relative to the wholecomponents of the top surface layer.
 15. A method for producing anelectrophotographic photosensitive element recited in claim 1, whichcomprises forming at least a photosensitive layer on anelectroconductive support to obtain the electrophotographicphotosensitive element, wherein a cyclic polysilane recited in claim 1is incorporated into at least a top surface of the electrophotographicphotosensitive element.
 16. An electrophotographic photosensitiveelement composition, which comprises a component for an outer surfacelayer of a photosensitive layer or a component for a surface protectionlayer of a photosensitive layer, and a cyclic polysilane recited inclaim
 1. 17. A composition according to claim 16, which comprises abinder, a cyclic polysilane, and at least one member selected from thegroup consisting of a charge-generating agent and a charge-transportingagent.
 18. A composition according to claim 17, wherein the bindercomprises a polycarbonate-series resin.
 19. An electrophotographiccartridge, which is provided with an electrophotographic photosensitiveelement recited in claim
 1. 20. An electrophotographic apparatus, whichis provided with an electrophotographic photosensitive element recitedin claim 1.